I can get free chickens but...

I have never raised chickens before but I can get 8 free barred rock chickens. They are 1-1/2 years old and moulting right now. I have a few questions.

What do the chickens eat? Do I need to buy feed or can I just let them roam around my yard/hay field?

I have an old barn that I could keep them in at night. I know I need to make sure it is totally closed so predators can't get in but what do I need to put in the barn for them (i.e. bedding, food, water, light, etc.)

Will they just lay their eggs in the barn wherver they want to or do I need to build/make a location for them?

Chickens will eat most anything. If you want to let them free-range (roam around your yard/hay field) provide them with a good laying formula that also includes the supplements they need (I use Purina). You will need a large shallow metal or ceramic pan to hold the feed. Don't use plastic--they can peck off bits and swallow them.
Chickens need a roost off the ground--a large wooden closet rod works fine. Ours use the rod during the day and roost on a roof beam at night. Provide a lower and a higher roost for them.
Their night coop needs to be secure both above and below. We used a stall in our barn, enclosed the openings all the way to the ceiling with chicken wire, dug down 18" and put chicken wire and bricks all around the bottom.
Chickens like nest boxes for laying eggs. Ours are about 23" square, three feet off the ground with a ladder going up to them. We have seven hens and four boxes, which is too many. Three boxes would be enough for you. Put hay, wood shavings, something in the nest boxes. The hens will toss most of it out, but that's entertainment for them!
Put "litter" in their coop--again, wood shavings, hay, or straw.
Chickens drink a lot--of water, that is! A clean source of water constantly available is necessary. We bought a large dog waterer--it has a 3 gal. bottle that flows into a shallow pan. Got it at Wal-Mart for about $15. Feed stores also have chicken waterers.
If your barred rocks are 18 months old, they are reaching the end of their prime egg-laying period. Older hens lay fewer eggs. I am assuming the eight are all hens. If a rooster is included, you will need to read up on chicks.
This is more than you ever wanted to know, I'm sure. Chickens are a lot of fun and very entertaining. Also, you get a lot of positive feedback from chickens because every day is a new, thrilling day for them!

Great advice from marlin, there. :) I'd just add that while yes, technically the hens are reaching the end of their most prolific laying period, they will still continue to lay, on average, an egg every other day or so for the next few years. I have hens that are nearing 9 years old that still lay every so often, and my 4-6 year old hens still lay regularly. So you should still get lots of eggs from them.

As for the molt, once they've grown back in new feathers it should be a matter of a week or two before they start laying again, usually. You can help speed up the process by offering them extra protein to help build new feathers--things like live mealworms (like candy for chickens!), crickets, scrambled eggs, cooked ground beef, etc. My hens seem to prefer the dark, covered, 'hidey-hole' type nest--chickens like to feel like they are hiding their eggs.

You'll have more questions as you go, so don't worry about posting them here. :) Also, I've got a chicken info site here that might help: